ZOJ 2836 Number Puzzle 题解

题面

lcm(x,y)=xy/gcd(x,y)
 lcm(x1,x2,···,xn)=lcm(lcm(x1,x2,···,xn-1),xn)

#include <bits/stdc++.h>
using namespace std;
long long n,m;
long long a[];
long long gcd(long long a,long long b)
{
    if(!b){
        return a;
    }
    return gcd(b,a%b);
}
long long lcm(long long a,long long b)
{
    return a*b/gcd(a,b);
}
int vis[];
long long ans=;
long long pre[];
void dfs(register int dep,long long goal,long long now)
{
    if(dep>goal){
        if(goal%==){
            ans-=(m/now);
        }
        else{
            ans+=(m/now);
        }
        return;
    }
    for(register int i=pre[dep-]+;i<=n;i++){
        if(!vis[i]){
            pre[dep]=i;
            vis[i]=;
            dfs(dep+,goal,lcm(now,a[i]));
            vis[i]=;
        }
    }
}
int main()
{
    freopen("div.in","r",stdin);
    freopen("div.out","w",stdout);
    cin>>n>>m;
    for(register int i=;i<=n;i++){
        cin>>a[i];
        ans+=(m/a[i]);
    }
    for(register int k=;k<=n;k++){
        dfs(,k,);
    }
    cout<<ans<<endl;
}